Now if I understand this correctly, If I can use the same 24 word seeds on my new Model T, then there won't be a fee for moving my coins over from the old Model One to the new Model T?
Correct.
If I can't safely figure that out, then my new Model T has a 12 word seed. If I just go with that, then there would be a fee for transferring from my old Model One to the new Model T?
Yes, you would have to pay a transaction fee.
Sorry again for having to keep figuring this out.. I'm just nervous about all this and afraid of losing coins somehow.
Hardly anything can go wrong. As long as you keep your Trezor One untouched, you will still have access to your coins.